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variable iv lengths for aes-gcm

DISCUSSION Ambarus Tudor-Dan-B38632 2 participants 4 messages Jun 18, 2015 – Jun 19, 2015 Crypto API

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Ambarus Tudor-Dan-B38632

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#0 lore raw

Hi Herbert,

I'm trying to find a method to pass IVs of various lengths to an algorithm. A particular case would be aes-gcm IV. It can have any number of bits between 1 and 2^64.

A possible way to do this is to set the ivlen per request. Are there any (better) ways to do this?

Thanks,
ta

maintainer
#1 lore raw
Quoted 7 lines · On Thu, Jun 18, 2015 at 10:43:18AM +0300, Ambarus Tudor-Dan-B38632 wrote:

I'm trying to find a method to pass IVs of various lengths to an algorithm. A particular case would be aes-gcm IV. It can have any number of bits between 1 and 2^64.

A possible way to do this is to set the ivlen per request. Are there any (better) ways to do this?

Why would you want do this apart from the fact that your hardware supports it and you want to export this?

Using a long IV is fundamentally insecure because all GCM will do is hash it and there is nothing that can guarantee uniquenes of the hash result.

You might as well just pull out a random number and use that as your IV.

Cheers,

Signature · 3 lines
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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#2 lore raw
Quoted 6 lines · Herbert Xu
Quoted 5 lines · On Thu, Jun 18, 2015 at 10:43:18AM +0300, Ambarus Tudor-Dan-B38632 wrote:

I'm trying to find a method to pass IVs of various lengths to an algorithm. A particular case would be aes-gcm IV. It can have any number of bits between 1 and 2^64.

Quoted 6 lines
Quoted 2 lines

A possible way to do this is to set the ivlen per request. Are there any (better) ways to do this?

Why would you want do this apart from the fact that your hardware supports it and you want to export this?

The reason is to cover a wide range of applications. Your question also applies to the gcm NIST publication.

Users may want to use a crypto module that meets the requirements of FIPS Pub. for various applications that use variable lengths for IV.

ta

maintainer
#3 lore raw
Quoted 6 lines · On Thu, Jun 18, 2015 at 12:44:06PM +0300, Ambarus Tudor-Dan-B38632 wrote:

The reason is to cover a wide range of applications. Your question also applies to the gcm NIST publication.

Users may want to use a crypto module that meets the requirements of FIPS Pub. for various applications that use variable lengths for IV.

What are these applications?

Cheers,

Signature · 3 lines
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt